Pressure filter having depending tubular filter elements

ABSTRACT

A pressure filter unit equipped with depending tubular filter elements comprising a tubular filter fabric element surrounding a rigid tubular liquid-permeable backing member, featuring an improved simple lead proof connection between the top ends of the filter elements and the supporting tube plate in the filter unit, which connection is resistant to backwash pressure supplied to the tubular filter elements through the upper open ends thereof.

United States Patent 1191 Miles, II 1451 Dec. 25, 1973 PRESSURE FILTERHAVING DEPENDING 1,578,314 3/1926 Herold 210 471 TUBULAR FILTER ELEMENTS#32231; 131132? fi*ll"' "213133; 5

, l es, 1'. Inventor: Harry Victor Miles, westport, 3,394,815 7/1968Harms et al. 210/333 x Conn. 3,419,151 12/1968 Smith et al 210/499 X[73] Assignee: Dorr-Oliver Incorporated, Stamford,

Conn. Primary Examiner-Frank A. Spear, Jr. [22] Filed, Apr 19 1972Attorney-Bunsen J. Kearns et al.

[21] App]. No.2 245,636

- Related u.s. Application um [57] BSTRACT [63] Continuation of Ser. No.54,216, July 13, 1970. A pressure filter unit equipped with dependingtubular filter elements comprising a tubular filter fabric ele- [52]U.S. Cl 210/333, 2l0/45Jldl2dlg4gl mem Surrounding a rigid tubularliquid pemeable [51] IntiCLf. 471 4/57 backing member, featuring animproved simple lead [58] d proof connection between the top ends of thefilter el- 21 I3 I g ements and the supporting tube plate in the filterunit, 3 I which connection is resistant to backwash pressure supplied tothe tubular filter elements through the [56] References Cited u r o nends thereof UNITED STATES PATENTS I ppe pe 1,683,786 9 1928 Long 210471 14 Claims, 15 Drawing Figures 'PMENIED 08125 I973 3.780.868

sum 2 UP 6 INVENTOR. HARRY v. MILES ww 2/4 {Q ATTORNEY.

PATENTEDmzs I975 SHEET 3 BF 6 F l G. 5

INVENTOR. HARRY v. MILES B {32? e ATTORNEY.

PATENTED08325 191s SHEET 8 or 6 INVENTOR. HARRY v. MILES vBY ATTORNEY.

3,780,868 SHEET 5 BF 6 PATENTEUUECZS I975 F I G. IO

INVENTOR. HARRY V. MILES ATTORNEY.

FIG. 8a

PATENTEDBEB251975 3; 780,868

SHEET 8 BF 6 FIG. H

INVENTOR. HARRY V. MILES ATTORNEY.

PRESSURE FILTER HAVING DEPENDING TUBULAR FILTER ELEMENTS This is acontinuation, of application Ser. No. 54,216, filed July 13, 1970.

This invention relates to pressure filters having depending tubularfilter elements contained in a pressurized filter tank.

ln this type of pressure filter, the upwardly open ends of the tubularfilter elements are connected to a tube plate which divides the tankinto a lower compartment receiving the pulp, sludge, or suspension to befiltered under pressure, and an upper compartment receiving the filtrateliquid passing through the tube plate and the upwardly open ends of thefilter elements.

The filter elements of the type herein contemplated comprise a tubularsleeve of filter material or filter cloth loosely surrounding a rigidtubular liquidpermeable or porous member the upper flanged end of whichtogether with the associated end of the filter sleeve must be sealinglyconnected to the tube plate of the filter unit.

More particularly, this invention relates to improvements in the tubularfilter elements themselves. One of the objects is to provide an improvedleak proof connection between the tube plate and the filter elements.Another object is to provide a simple and inexpensive filter sleeveadapted to provide said leak proof connection.

The underlying problem and the objects of this invention will be morereadily understood by reference to the US. Pat. to Miles No. 3,356,215disclosing and describing a filtration-thickening unit herein shown forthe purpose of illustration to embody this invention. Such a filter unitcomprises a number of pressure filtration zones arranged in parallel,each zone comprising a group of said depending filter elements. Thesezones may be operated in a filtration cycle whereby the filter elementsin one zone at 'a time, are subjected to backwashing, while the filterelements in all the other zones continue under conditions of pressurefiltration. hasmuch as filtration and backwashing thus proceedsimultaneously in this filter unit, backwash liquid must be supplied tothe filtration zones sequentially at a pressure greater than thefiltration pressure. During backwashing, the layer of sludge solidscollected on the respective filter elements is released or dislodged andsinks to the bottom of the tank, whence the collected thickened mattermay be withdrawn periodically.

More particularly, in the filter-thickening unit herein exemplified eachof the pressure filtration zones comprises a group of depending tubularfilter elements having their upper ends connected to a tube plate sothat filtrate liquid forced into the interior of the filter elementswill pass upwardly through the tube plate from each filtration zone intoa separate filtrate receiving chamber, while a layer of sludge solidsbuilds up externally upon the filter elements. A hollow cover membercooperating with the tube plate is subdivided by radial partitionsdefining said separate filtrate receiving chambers. These chambers inturn define the number of the pressure filtration zones in the tank. Avalve chamber mounted atop the radially partitioned cover membercontains a rotating valve conduit or duct connected to a supply of washliquid under pressure. Rotation of this valve duct supplies the washwater sequentially to each of the chambers in the cover member, and thussequentially to the groups of filter elements in the respectivefiltration zones. Thus in the operating cycle of this machine, each ofthe pressure filtration zones is subjected to a period of backwashing,while pressure filtration continues in all of the other zones. Feedsuspension under pressure-is supplied continuously to the tank, whilefiltrate liquid discharges continuously through the valve chamber whichhouses the rotating duct.

In the aforementioned patent to Miles, the porous rigid tube of thefilter element has a flange at its upper end. The upper end of thefilter sleeve surrounding the tube is connected to a flanged member offlexible rubber material having a neck portion peripherally connected asby sewing to the filter cloth material of the filter sleeve. When thiscomposite filter element is in place, both the rigid flange of theporous tube and the flexible flange or gasket are confined or compressedbetween the top face of the tube plate and a sectorshaped retainerplate, thus securing all the filter elements communicating with therespective sectorshaped filtrate receiving chamber. I This earliermanner of mounting and securing the filter element was subject toleakage with ensuing turbidity of the filtrate liquid, due to the rubbergasket developing a compression set, or due to an occasional rupturepartially severing the aforementioned shaped gasket member from thematerial of the filter sleeve.

This invention avoids such leakage or rupture, by the provision of afilter sleeve having its upper open end specially prepared with anannular bead radially overhanging from the sleeve, said bead b'eingconfined between the tube plate and the retainer plate. More inparticular, this bead comprises a ring member of noncompressiblematerial enclosed or enveloped by the upper terminal portions of thefilter sleeve material or filter cloth itself. The filter clothenveloping the noncompressible ring member provides an effective andlonglasting seal against leakage, eliminating the causes of compressionset or rupture.

in a practical embodiment a filter cloth material in forming the filtersleeve is employed in such a manner that the threads of the fabricextend spirally relative to the longitudinal sleeve axis, thus renderingthe sleeve expandable, thereby allowing the ring member to be insertedinto the sleeve, even though the ring diameter is substantially greaterthan the sleeve.

The inserted ring member is positioned in a plane transversal of thesleeve axis, forming an outward annular bulge in the transverselystretchable filter sleeve. The non-extended free end portion of thefilter material is turned inwardly through the ring member and securedto the adjoining surrounding portion of the filter sleeve material belowthe ring. The non-compressible ring member thus enveloped by thetransversely stretched filter media forms a radially outwardlyoverhanging bead which when compressed prevents leakage and avoidsrupture.

Specific features lie in the provision of a simple and inexpensivefilter sleeve wherein the filter cloth of the sleeve is expandable, andin a method for making such a sleeve.

As this invention may be embodied in several forms without departingfrom the spirit or essential characteristics thereof, the presentembodiment is illustrative and not restrictive. The scopeof theinvention is defined by the appended claims rather than by thedescription preceding them, and all embodiments which fall within themeaning and range of equivalency of the claims are therefore intended tobe embraced by those claims.

FIG. 1 is a vertical sectional view of the filtrationthickening unitembodying the invention, provided with the rotary valve conduit forbackwashing the filter elements.

FIG. 2 is an enlarged view of the top end portion of the filter unit,more clearly showing the main components of the unit.

FIG. 3 is a cross-section taken on line 3-3 of FIG. 2, showing therotary valve conduit and associated flow passages.

FIG. 4 is a part-sectional view taken on line 4-4 in FIG. 3, furtherillustrating the function of the rotary valve conduit.

FIG. 5 is a detail cross-section of the valve conduit, taken on line 5-5in FIG. 4.

FIG. 6 is a cross-sectional view taken on line 6-6 of FIG. 2,illustrating the cover member of the filter unit, radially partitionedto provide sector-shaped filtrate receiving chambers.

FIG. 7 is a partial cross-sectional view taken on line 7-7 in FIG. 2,illustrating the disposition of the tubular filter elements in thesupporting tube plate.

FIG. 8 is a greatly enlarged vertical sectional detail view of thetubular filter element secured in place, featuring the speciallyprepared beaded end of the filter sleeve.

FIG. 9 shows the filter sleeve incomplete, featuring a filter clothstreatchable transversely as well as longitudinally due to the spiraldirection of the thread.

FIG. 10 shows a blank strip of the filter material to be formed into thefilter sleeve of FIG. 9.

FIG. 11 illustrates a manner of preparing the blank strip of the filtercloth material of FIG. 10.

FIGS. l2, l3, l4 illustrate phases of progression in the preparation ofthe beaded end of the filter sleeve.

In the embodiment illustrated in FIG. 1 the filtrationthickeningapparatus comprises three main sections A, B, C.

Section (A) of the apparatus comprises a cylindrical tank 10 supportedon legs 11. In the tank bottom is mounted a variable-speed motor-drivenagitator mechanism 12 for maintaining a bed S of heavy thickened sludgein a flowable condition for withdrawal through a control valve 120provided in a discharge connection 12b. A lateral manhole 13 as well asvarious tap connections 13a are provided on the tank. A supplyconnection 14 with valve 14a for introducing the solids suspension to bethickenedunder pressure is provided near the top of the tank, deliveringinto a feed distributing conduit 14b which may extend peripherally alongthe inner surface of the tank, with discharge openings 14c spaced alongthis conduit.

The top end of the tank itself is closed by a plate member 15 to whichare removably connected the upper ends of the numerous depending tubularfilter elements 16 upon which a layer of suspension solids may be formedwhile filtrate liquid passes from the interior of these elementsupwardly through the plate. The closed lower ends of the filter elementsterminate a distance D from what is indicated to be the potentialmaximum level L of the bed of settled thickened sludge, that distancebeing adequate to allow for the lumps or fragmented layer of solids whenreleased from the filter elements to fall onto or into the bed ofsludge.

Section (B) of the apparatus comprises a hollow cover or dished covermember 17 overlying the plate member 15 and marginally fastened theretoand to the top end of the tank by means of quick removable screw clamps18. This cover member 17 has internal radial partitions l9 defining withthe plate member 15 a cluster of sector-shaped filtrate receivingchambers 20 (see FIG. 6) disposed aroundthe vertical axis of the tank.The inner narrow ends of these receiving chambers are bounded by acylindrical vertical wall or tubular partition 21 which itself defines acentral chamber 22 (see FIGS. 2 & 6). The cover member 15, and the topend of the tank with the plate 15 between them are held tightly togetherby means of the screw clamps 18. The assembly and the relationship ofthe parts is such that the bottom edges of the radial partition means inthe cover member close tightly upon the plate member 15.

Penetrating each filtrate receiving chamber 20 is a vertical anchoringbolt 23 for further securing the cover member and the bottom edges ofthe partition means tightly upon the plate member 15. Each chamber 20further has a tap 24 with closure valve 25 through which the filtrateliquid from each of the chambers 20 may be sampled for testing of itsclarity or turbidity as an indicator of possible defectiveness of anyfilter elements in the respective group served by the receiving chamber20 being tested.

The dished and partitioned cover member 17 is formed at the top with acentral horizontal plate portion 26 provided with ports 27, one for eachchamber 20. These ports 27 are arranged in a circle around the verticalaxis of the tank (see also FIG. 3), providing communication between eachchamber 20 and the aforementioned filtrate collecting and backwashingsection (C) mounted atop the cover member 17. This cover member furtherhas external eyes 28 whereby the entire top assembly comprising sections(B) and (C) may be conveniently lifted off the tube plate 15 afterremoval of the screw clamps 18, for inspection of the filter elements.The mounting of the improved filter elements themselves and theirparticular construction will be described in more detail below.

In Section (C) a casing structure 29 for collecting the filtrate liquidfrom the chambers 20 provides a filtrate collecting chamber 29a, and ishere shown to comprise a cylindrical body portion 30 having a filtratedischarge connection 30a and a top cover plate 31 fastened thereto. Awear plate 32 at the bottom of this casing structure is here indicatedas part of section (C). This plate is interposed between the bottom faceof casing structure 29 and the top face of cover member 17, the partsbeing bolted together tightly in face-to-face relationship to oneanother. The wear plate has ports 33 of trapezoidal shape (see FIG. 3)in general registering with ports 27 in the cover member 17.

Within the casing structure 29 or filtrate collecting chamber 29a ismounted a distributing mechanism 34 operable to supply a reverse flow ofbackwash pressure liquid, preferably the filtrate liquid itself,sequentially to the chambers 20 in repetitious cycles. One of thechambers 20 at a time, and the group of filter elements communicatingtherewith are subjected to backwashing, while the other groups of filterelements as defined by the other chambers 20, are being subjected topressure filtration.

The mechanism 34, according to the present example, comprises a rotaryconduit member or rotary valve fixed to a vertical shaft 36 actuated asby motorized variable speed drive means 37 for rotating the conduitmember so that an inclined radial conduit passage 38 in valve member 35is placed in flow communication sequentially with chambers 20 forpassing backwash liquid downwardly thereto as indicated by arrows R-l,while filtrate liquid passes upwardly in the direction of arrow R-2 fromthose other chambers 20 not communicating with the backwash conduitpassage 38. This passage while rotating communicates at all times withan inverted annular supply channel 39 formed by a stationary annularheader 40 surrounding the shaft and having planar face-to-face contactwith the top face of the rotary conduit member 35. This annular headerhas a neck 41 communicating through a flexible tubular joint 42 with aninlet 43 which is part of casing structure 29.

The vertical shaft 36 is keyed or splined to the conduit member andslideable therein to a small extent while rotating freely in the annularheader 40. The shaft extends upwardly through the top plate 31 by way ofa suitable seal or stuffing box 44. This shaft has a lower end portion45 projecting through wear plate 32 into the central chamber 22. Acompression coil spring 46 surrounding this lower shaft end portion isconfined between stop nuts 47 and the wear plate 32, urging the annularheader 40 into planar operating contact with the rotary conduit member,and the conduit member 35 into planar operating contact with the wearplate 32. The spring pressure is thus effective through a sleeve 48fixed on the shaft, acting on a vertical thrust ball bearing 49.

The rotary flow conduit member as shown in the embodiment of FIGS. 3 and4 has smoothly machined parallel top and bottom faces F-l and F2respectively, in operating contact with similarly treated faces of theannular header 40 and the wear plate 32. This rotary conduit member orcasting comprises a basic shape or body portion in the form of a hollowtrunco-conical body 50 (see also FIGS. 2 and 3) open at the bottom butclosed at the top except for the inlet opening of an inclined flowconduit portion 51 interrupting the basic trunco-conical shape. Theinclined conduit itself has an inflow area A-1 and an outflow area A-2.Internally the trunco-conical hollow body portion is formed with a hubportion 52 keyed or splined to shaft 36, so as to be slideable thereinto a small extent.

From the top plan view of the conduit member in FIG. 3 it will be seenthat the inclined conduit portion 51 therein juts out a distance (T)beyond the base diameter M of the trunco-conical body portion.Horizontal arcuate wing portions 53 and 54 extend laterally in oppositedirections from the lower end of the conduit portion 51, the wingportion being integral also with the bottom end of the trunco-conicalshape. These wing portions together with the conduit portion 51 form aradially projecting arcuate portion 55 (see FIG. 3). The wing portions53 and 54 serve as blank-off portions effective to allow for shifting ofthe valve conduit from one port 33 to the next without short-circuiting.

A preferred embodiment of the improved filter element is described asfollows by reference to FIGS. 8 to 14.

The embodiment in FIG. 8 shows that the filter element comprises a rigidtube 65 of substantial wall thickness, consisting of a porousliquid-permeable material, for example a porous polypropylene materiallargely resistant to the effect of chemicals and the effect of heat. Theupper end of this porous tube has fixed thereto a flange a, while thelower end is closed by an end piece 66 bonded to the tube and havingperforations 67.

Surrounding the porous tube is a sleeve 68 of filter media material orcloth, prepared so as to be stretchable in a transverse as well aslongitudinal direction. The lower end of this sleeve is closed by a seamor stiching 69, thus forming a small downwardly pointed pocket 70 belowthe lower end of the porous tube.

This filter sleeve has an upper end portion in the form of a bead 71formed in a special manner provided for by this invention, andconstituting an outwardly overhanging rim. The bead comprises arelatively rigid ring 72 in the form of an O-ring, that is a ring ofcircular cross-sectional profile. This rigid ring consisting of asubstantially non-compressible material or plastic is enveloped by theupper end portion of the filter cloth in such a manner that the cloth isstretched or expanded around the ring, and then turned inwardly over thering, thus terminating within the sleeve. The turned-in portion of thefilter material is fastened as by stiches 73 to the adjoining portion ofthe filter sleeve material 73a, that is peripherally along a line belowand close to the bead.

When the filter element is mounted and in place in the above describedpressure filter unit, the bead portion of the filter sleeve (see FIG. 8)is confined between the tube plate 15 and the flange 65a of the poroustube, both the bead portion of the sleeve and the flange being in turnpressed down by a retainer plate 74 bolted to the tube plate 15.

Turbidity of the filtrate liquid due to leakage from the filtrationzones through the tube plate is prevented by the sealing effect of thefilter cloth enveloping the ring preferably consisting of anon-compressible composition material or plastic. From the greatlyenlarged detail showing of the bead in FIG. 8a it may be seen that anyleakage through the space between the tube plate and the ring isprevented by the action of the interposed compressed filter clothmaterial enveloping the ring. Leakage through the space between the ringand flange 65a of the porous tube is similarly prevented by the actionof the interposed filter cloth material.

Optimum sealing effect is attainable at the upper point P-1 and thelower point P-2 due to what may be roughly considered as line contactpressure relationship at the top and at the bottom of the ring.

For purposes of this invention, the filter sleeve is stretchable in bothdirections, that is transversely as well as longitudinally. Such two-waystretchability is attainable by providing a strip or blank 75 of filtercloth material (see FIG. 10) wherein the threads of the weave areoriented in a diagonal direction. That is to say, the threads betweenthemselves intersect at an angle of about 45 with the longitudinal edgesE-l and E-2 of this strip of filter cloth.

This strip of filter cloth material is formed or rolled into a tube orsleeve 8-1 see FIG. 9) with a longitudinal seam or seams S-2interconnecting the overlapping longitudinal edge portions B3 and E-4 ofthe filter cloth. In this way, the threads of the weave now becomespirally oriented relative to the axis of the sleeve, while the lowerend of the sleeve is closed by the aforementioned transverse seam 69.

FIGS. l2, l3, and 14 illustrate the procedure whereby the beaded endportion is formed upon the upper end of the partly finished filtersleeve of FIG. 9.

A first phase of the procedure shown in FIG. 12 is the inserting of thering 72 into the upper end portion of the partly finished filter sleeve.

A second phase as shown in FIG. 13 is the levelling of the ring withinthe sleeve to a horizontal position, or a position transversely of theaxis of the sleeve. This involves expanding the sleeve material so thatit will form an annular outward bulge 76 accommodating therein the ringa distance I from the top edge 76a of the sleeve. A third phase shown inFIG. 14 involves turning the upper free non-expanded end portion of thefilter cloth material inwardly through the ring, and fastening orstitching the turned-in portion in place as indicated by a peripheralseam 77 located below and close to the ring, thus fully enveloping thering in the filter cloth material. In this way, the head portionrepresents an outwardly directed annular overhang.

The finished filter sleeve or sock may then be slipped onto, or pulledover the porous tube, with the turned-in end portion 78 of the materialoffering no obstruction. This assembly of a filter element including theporous tube 65 and the sleeve is then inserted through a respective holein the tube plate 15 of the filter unit, with the outer continuous faceof the sleeve material allowing for smooth insertion. The retainer plate74 is then applied and bolted to the tube plate, rendering the sealingpoints P-1 and P-2 (see FIG. 8a) effective in all the connections of thefilter elements covered by this retainer plate.

I claim:

1. In a pressure filter of the type having depending tubular filterelements exposed to a pulp to be filtered under pressure, and deliveringfiltrate liquid from the upper open end,

the combination which comprises a horizontal tube plate having holes forthe insertion therein of tubular filter elements,

a filter element inserted in said tube plate, which comprises aliquid-permeable rigid tube having an upper open end provided with aflange,

a filter sleeve having a closed end and an open end, surrounding saidtube, and consisting of a filter media constructed and arranged so as tobe radially expandable from its normal diameter,

a ring of substantially non-deformable material, said ring having aninner diameter substantially equal to the diameter of the sleeve,inserted into said open end so that said media is stretched radiallyabout said ring, accommodating the ring in a plane perpendicular to thelongitudinal axis of the sleeve, the unstretched open end portion of thesleeve being turned inwardly through said ring, and connectedperipherally to the adjoining surrounding portion of said sleeve thusforming an annular outwardly overhanging terminal bead at said open end,confined between said tube plate and said flange,

retainer means engaging the top side of said flange,

and means for securing said retainer means relative to said tube platewhereby said bead is compressed in such a manner that the filter mediaenveloping said ring provides a pair of annular compression sealseffective between said ring and said tube plate, and between said ringand said flange respectively.

2. The combination according to claim 1, wherein the filter sleevematerial comprises a length of filter fabric having longitudinal edges,with the threads of the weave intersecting substantially at rightangles, but oriented diagonally to said edges, said edges beinginterconnected to constitute said sleeve.

3. The combination according to claim 1, wherein the filter sleevematerial consists of a weave having threads normally intersectingsubstantially at right angles, but extending in a spirally orienteddirection relative to the axis of the longitudinal filter element,whereby said filter sleeve is rendered radially expandable.

4. The combination according to claim 1, wherein said ring is ofcircular cross-sectional profile, whereby the compression effective insaid annular seals is concentrated along a relatively narrow annularzone.

5. The combination according to claim 1, wherein said retainer meanscomprises a retainer plate, constructed and arranged for securing aplurality of said filter elements. 1

6. A tubular filter element which comprises a liquid permeable rigidtube having an upper open end provided with a flange,

a filter sleeve having a closed end and an open end, surrounding saidtube, and consisting of a filter media constructed and arranged so as tobe radially expandable from its normal diameter,

a ring of substantially non-deformable material, having an innerdiameter substantially equal to the diameter of the sleeve, insertedinto said open end so that said media is stretched radially about saidring, accommodating the ring in a plane perpendicular to thelongitudinal axis of the sleeve, the unstretched open end portion of thesleeve being turned inwardly through said ring, and connectedperipherally to the adjoining surrounding portion of said sleeve, thusforming an annular outwardly overhanging terminal bead adjoining saidflange.

7. The filter element according to claim 6, wherein the filter sleevematerial consists of a weave having threads normally intersectingsubstantially at right angles, but extending in a spirally orienteddirection relative to the axis of said filter element, whereby saidfilter sleeve is rendered radially expandable.

8. The filter element according to claim 6, wherein said ring is ofcircular cross-sectional profile.

9. The filter element according to claim 6, wherein the filter sleevematerial comprises a length of filter fabric having longitudinal edges,with the threads of the weave intersecting substantially at rightangles, but oriented diagonally to said edges, said edges beinginterconnected to constitute said sleeve.

10. The method of making a filter sleeve for the prupose substantiallysuch as herein described, which comprises,

providing a length of filter cloth that is stretchable transversely ofits longitudinal extent,

interconnecting the longitudinal edge portion of said length of filtercloth in such a manner as to form a tubular shape representing a partlyfinished sleeve,

closing one end of said tubular shape,

providing a ring of substantially non-deformable material, and having aninner diameter substantially equal to the diameter of the sleeve,

inserting and positioning said ring in the open end of said partlyfinished sleeve, whereby said filter cloth is radially stretched toaccommodate said ring in a plane extending transversely of said sleeve,

turning the unstretched free end portion of the filter cloth inwardlythrough the ring,

and connecting said turned-in portion peripherally to the adjoiningsurrounding portion of the sleeve, so that there is formed a beadradially outwardly overhanging from said filter media.

11. The method according to claim 10, wherein said ented directionrelative to the longitudinal axis of the sleeve, whereby said sleeve isradially expandable beyond its normal diameter,

length of filter cloth is provided from a larger piece of 10 clothhaving a weave wherein the threads intersect at right angles, by cuttingsaid cloth on the bias relative to the direction of said threads, andinterconnecting the longitudinal edges of said cloth.

a circular uninterrupted ring member consisting of substantiallynon-deformable material, having an inner diameter substantially equal tothe diameter of the sleeve, inserted into said open end of the ring sothat the fabric expands hugging said ring in an annular bulge extendingin a plane perpendicular to the longitudinal axis of the sleeve, andformed between the directly adjoining unexpanded portions of the sleeve,the unstretched open end portion of the sleeve being turned inwardlythrough said ring, and connected peripherally to the thus adjoiningunexpanded surrounding portion of said sleeve, to constitute acontinuous beaded flange, the diameter of the annular center line ofsaid ring being substantially greater than the outside diameter of thesleeve, and large enough to provide mutually opposed unbroken annulartransverse sealing faces of sleeve material at the top and at the bottomof said beaded flange.

13. The filter sleeve according to claim 12, wherein 14. The filtersleeve according to claim 12, wherein said ring member is of circularcross-sectional profile.

1. In a pressure filter of the type having depending tubular filterelements exposed to a pulp to be filtered under pressure, and deliveringfiltrate liquid from the upper open end, the combination which comprisesa horizontal tube plate having holes for the insertion therein oftubular filter elements, a filter element inserted in said tube plate,which comprises a liquid-permeable rigid Tube having an upper open endprovided with a flange, a filter sleeve having a closed end and an openend, surrounding said tube, and consisting of a filter media constructedand arranged so as to be radially expandable from its normal diameter, aring of substantially non-deformable material, said ring having an innerdiameter substantially equal to the diameter of the sleeve, insertedinto said open end so that said media is stretched radially about saidring, accommodating the ring in a plane perpendicular to thelongitudinal axis of the sleeve, the unstretched open end portion of thesleeve being turned inwardly through said ring, and connectedperipherally to the adjoining surrounding portion of said sleeve thusforming an annular outwardly overhanging terminal bead at said open end,confined between said tube plate and said flange, retainer meansengaging the top side of said flange, and means for securing saidretainer means relative to said tube plate whereby said bead iscompressed in such a manner that the filter media enveloping said ringprovides a pair of annular compression seals effective between said ringand said tube plate, and between said ring and said flange respectively.2. The combination according to claim 1, wherein the filter sleevematerial comprises a length of filter fabric having longitudinal edges,with the threads of the weave intersecting substantially at rightangles, but oriented diagonally to said edges, said edges beinginterconnected to constitute said sleeve.
 3. The combination accordingto claim 1, wherein the filter sleeve material consists of a weavehaving threads normally intersecting substantially at right angles, butextending in a spirally oriented direction relative to the axis of thelongitudinal filter element, whereby said filter sleeve is renderedradially expandable.
 4. The combination according to claim 1, whereinsaid ring is of circular cross-sectional profile, whereby thecompression effective in said annular seals is concentrated along arelatively narrow annular zone.
 5. The combination according to claim 1,wherein said retainer means comprises a retainer plate, constructed andarranged for securing a plurality of said filter elements.
 6. A tubularfilter element which comprises a liquid permeable rigid tube having anupper open end provided with a flange, a filter sleeve having a closedend and an open end, surrounding said tube, and consisting of a filtermedia constructed and arranged so as to be radially expandable from itsnormal diameter, a ring of substantially non-deformable material, havingan inner diameter substantially equal to the diameter of the sleeve,inserted into said open end so that said media is stretched radiallyabout said ring, accommodating the ring in a plane perpendicular to thelongitudinal axis of the sleeve, the unstretched open end portion of thesleeve being turned inwardly through said ring, and connectedperipherally to the adjoining surrounding portion of said sleeve, thusforming an annular outwardly overhanging terminal bead adjoining saidflange.
 7. The filter element according to claim 6, wherein the filtersleeve material consists of a weave having threads normally intersectingsubstantially at right angles, but extending in a spirally orienteddirection relative to the axis of said filter element, whereby saidfilter sleeve is rendered radially expandable.
 8. The filter elementaccording to claim 6, wherein said ring is of circular cross-sectionalprofile.
 9. The filter element according to claim 6, wherein the filtersleeve material comprises a length of filter fabric having longitudinaledges, with the threads of the weave intersecting substantially at rightangles, but oriented diagonally to said edges, said edges beinginterconnected to constitute said sleeve.
 10. The method of making afilter sleeve for the prupose substantially such as herein described,which comprises, providing a length of filter cloth that is stretchabletransversely of its longitudinal extent, interconnecting thelongitudinal edge portion of said length of filter cloth in such amanner as to form a tubular shape representing a partly finished sleeve,closing one end of said tubular shape, providing a ring of substantiallynon-deformable material, and having an inner diameter substantiallyequal to the diameter of the sleeve, inserting and positioning said ringin the open end of said partly finished sleeve, whereby said filtercloth is radially stretched to accommodate said ring in a planeextending transversely of said sleeve, turning the unstretched free endportion of the filter cloth inwardly through the ring, and connectingsaid turned-in portion peripherally to the adjoining surrounding portionof the sleeve, so that there is formed a bead radially outwardlyoverhanging from said filter media.
 11. The method according to claim10, wherein said length of filter cloth is provided from a larger pieceof cloth having a weave wherein the threads intersect at right angles,by cutting said cloth on the bias relative to the direction of saidthreads, and interconnecting the longitudinal edges of said cloth.
 12. Afilter sleeve having an open top end and a closed bottom end, adapted tobe fitted over a liquid permeable rigid tube, and to be subjected toexternal liquid filtration pressure, said filter sleeve consisting of afilter fabric having a weave of threads normally intersectingsubstantially at right angles, but extending in a spirally orienteddirection relative to the longitudinal axis of the sleeve, whereby saidsleeve is radially expandable beyond its normal diameter, a circularuninterrupted ring member consisting of substantially non-deformablematerial, having an inner diameter substantially equal to the diameterof the sleeve, inserted into said open end of the ring so that thefabric expands hugging said ring in an annular bulge extending in aplane perpendicular to the longitudinal axis of the sleeve, and formedbetween the directly adjoining unexpanded portions of the sleeve, theunstretched open end portion of the sleeve being turned inwardly throughsaid ring, and connected peripherally to the thus adjoining unexpandedsurrounding portion of said sleeve, to constitute a continuous beadedflange, the diameter of the annular center line of said ring beingsubstantially greater than the outside diameter of the sleeve, and largeenough to provide mutually opposed unbroken annular transverse sealingfaces of sleeve material at the top and at the bottom of said beadedflange.
 13. The filter sleeve according to claim 12, wherein the filtersleeve material comprises a length of filter fabric having longitudinaledges, with the threads of the weave intersecting substantially at rightangles, but oriented diagonally to said edges, said edges beinginterconnected to constitute said sleeve.
 14. The filter sleeveaccording to claim 12, wherein said ring member is of circularcross-sectional profile.